Hey Harsh!
If you have set a specific home page for the anonymous users but the anonymous user don't have enough rights to access all the resources they will see the sign-in page, as you can read here:
https://docs.mendix.com/refguide/navigation/?_gl=1*vatz6j*_ga*MTcxNTk5NzgwNy4xNjk2OTQyOTE1*_ga_4PE2C4QFC7*MTcwMDU1NjUxNi40NjcuMS4xNzAwNTU3NTk5LjU2LjAuMA..#:~:text=4.3-,Authentication,-If%20an%20anonymous
The sign in page is the one that you have configured on the navigation: